Greenhouse climate control affects postharvest tomato quality

In this study, important quality properties such as firmness, sugar and acid levels were measured andanalysed in tomatoes harvested from three greenhouses during a five month period and stored at 16◦Cfor over 20 days. Tomatoes were harvested from three identical, neighbouring, greenhouses which wereeither conventionally ventilated (open greenhouse) or mechanically cooled (semi-closed greenhouses).Sugar and acids levels were hardly affected by greenhouse type. Compared to the open greenhouse, semi-closed greenhouses produced heavier and less mature (firmer) fruit at the commercial harvesting stagebased on colour. Fruit maturity differences could be linked to the vertical temperature gradient and to CO2levels in the different greenhouses. This indicates that CO2levels and temperature affect the synchroni-sation between colour and firmness maturity at harvest. The acceptance period, i.e., the time period bothtomato colour and firmness are considered acceptable by consumers, will likely be positively affectedwhen growers switch from conventionally ventilated to semi-closed production systems. Additional togreenhouse effects also effects of the harvest month were observed. The sugar to acid ratio was highest andglucose to fructose ratio was lowest in July, the month with the highest irradiance, irrespective of green-house type. The estimated value for the maximum firmness (Fmax) varied from 17.9 N in August to 31.2 Nin June. This monthly variation in Fmaxexplains an important part of the variation found in the posthar-vest behaviour of tomatoes. Interestingly, the monthly variation in Fmaxshowed the same trend as foundfor the monthly initial sugar levels. It might be hypothesised that the monthly variation in glucose andfructose levels causes variation in that part of firmness that is generated by cell turgor. The monthly vari-ation in Fmax, sugar and acid levels could not be linked to climate conditions and remains to be elucidated.